The invention relates to a method and a device for position detection of an object which can be moved along an acoustic-signal conductor of ferromagnetic material, particularly of a lift cage which can be moved along a vertical shaft. Such a method and device may be used for controlling the position of a lift cage or the like and thus ensuring a correct positioning at predetermined stops according to floor levels.
From European Patent No. EP 1 065 517 A1, a device for detecting the position of a lift cage moving along a vertical shaft by means of a ferromagnetic acoustic signal conductor extended vertically in the shaft and having a predetermined, essentially uniform, velocity of sound propagation and with a signal input coupler connected to a signal transmitter and located at the lift cage for incoupling an acoustic signal into the acoustic signal conductor is known. In this arrangement, a signal output coupler, which is connected to an evaluating circuit for generating a signal representative of the instantaneous position of the lift cage, is arranged adjacent to at least one end of the acoustic signal conductor. The acoustic signal conductor may have an acoustic-signal attenuator at least at one end. The signal input coupler can be triggered by the evaluating circuit at time intervals which are of such a magnitude that no superpositions with previous acoustic signals incoupled by the signal input coupler and subsequently reflected at the ends of the acoustic-signal conductor occur.
A similar device for position detection in which calibrating signals are additionally incoupled into the acoustic-signal conductor is known from German Patent No. DE 199 03 644 C1. A further device for measuring the length of a measured length from a predetermined point to an object which can be moved along the measured length is known from published German Patent Application No. DE 100 06 379 A1, the object exhibiting two signal input couplers for acoustic signals.
It has been found in such devices for position detection that problems occur with respect to the acoustic-signal transmission to the signal output coupler in the case of relatively great lengths of the acoustic-signal conductor. More detailed investigations revealed that due to the fact that a magnetic field which flows through the acoustic-signal conductor is generated by the signal input coupler for incoupling the acoustic signal, a small residual field which leads to the attenuation of acoustic signals remains due to remanence. Although this is of the order of magnitude of 15 to 30xc3x9710xe2x88x926 Nepers/m, it in the end leads to the fact that the acoustic signal can be attenuated by up to more than 50% with a length of 130 m of the acoustic-signal conductor.
It is an object of the invention to provide a method for the detection of the position of an object moveable along an acoustic-signal conductor of ferromagnetic material which make it possible to prevent a significant acoustic-signal attenuation due to the acoustic-signal conductor even with great lengths of the acoustic-signal conductor.
It is a further object of the invention to provide a device for the detection of the position of an object moveable along an acoustic-signal conductor of ferromagnetic material which make it possible to prevent a significant acoustic-signal attenuation due to the acoustic-signal conductor even with great lengths of the acoustic-signal conductor.
It is a further object of the invention to provide a position detection for a lift cage with increased precision.
The invention concerns a method for detecting the position of an object moveable along an acoustic-signal conductor of ferromagnetic material, comprising the steps:
incoupling an acoustic signal in a clocked manner into the acoustic-signal conductor by means of a signal input coupler connected to a signal transmitter;
extracting the incoupled signal by means of a signal output coupler; and evaluating the extracted signal by an evaluating circuit for generating a signal representative of the instantaneous position of the object;
wherein after the acoustic signal has been incoupled, an opposite magnetic field is applied for compensating for the residual magnetization originating from the incoupling of the acoustic signal.
The invention further concerns a method for detecting the position of an object moveable along an acoustic-signal conductor of ferromagnetic material, comprising the steps of:
incoupling an acoustic signal in a clocked manner into the acoustic-signal conductor by means of a signal input coupler connected to a signal transmitter;
extracting the incoupled signal by means of a signal output coupler; and evaluating the extracted signal by an evaluating circuit for generating a signal representative of the instantaneous position of the object;
wherein in each case after the acoustic signal has been incoupled, a number of acoustic compensation signals having the opposite phase to the incoupled acoustic signal are incoupled at the beginning and subsequently in each case with changing phases and decreasing amplitude.
The invention further concerns a device for detecting the position of an object moveable along an acoustic-signal conductor of ferromagnetic material, comprising a signal input coupler connected to a signal transmitter for the clocked incoupling of an acoustic signal into the acoustic-signal conductor and a signal output coupler which is connected to an evaluating circuit for generating a signal representative of the instantaneous position of the object, wherein in each case after the incoupling of the acoustic signal, an opposite magnetic field can be incoupled for compensating for the residual magnetization originating from the incoupling of the acoustic signal.
The invention further concerns a device for detecting the position of an object moveable along an acoustic-signal conductor of ferromagnetic material, comprising a signal input coupler connected to a signal transmitter for the clocked incoupling of an acoustic signal into the acoustic-signal conductor and a signal output coupler which is connected to an evaluating circuit for generating a signal representative of the instantaneous position of the object, wherein in each case after incoupling of the acoustic signal, a sequence of a number of acoustic compensation signals with opposite phase to the incoupled acoustic signal can be incoupled at the beginning and subsequently in each case with changing phases and decreasing amplitude.
In this arrangement, a compensation energy associated with the incoupled acoustic signal is incoupled into the acoustic-signal conductor, which generates a coercive force which has the effect that the acoustic-signal conductor residually magnetized by the incouplion of the acoustic signal is substantially demagnetized or this magnetic field is substantially overcompensated for to form a corresponding magnetic field in the opposite direction. In the first case, the compensation energy follows the incoupled acoustic signal and essentially leads to a demagnetization. The result is that the attenuation is  less than 10xe2x88x926 Nepers/m so that even with great lengths of the acoustic-signal conductor or the use of an acoustic signal reflected at one end of the acoustic-signal conductor, the attenuation remains small enough to ensure correct extraction by the signal output coupler. In the second case, overcompensation or opposite magnetization takes place to such an extent that an acoustic signal incoupled later finds an acoustic-signal conductor with a magnetic field of opposite direction and magnitude to that generated by itself so that the attenuation of the acoustic signal propagating through the acoustic-signal conductor also remains correspondingly small in this case. This compensation or overcompensation is suitably used for any type of incoupled acoustic signals, whether they are used, for example, for measuring, calibration or the like.
The compensation energy can be introduced, for example, by heating to the Curie temperature, mechanical knocking or magnetic fields and, in particular, by at least one acoustic compensation signal following the acoustic signal.
For the acoustic signals, a signal input coupler is provided which either can be arranged in a fixed position at one end of the acoustic-signal conductor, while a corresponding signal output coupler is arranged on the moving object, for instance a lift cage, or which is arranged on the moving object, while the signal output coupler is stationary in the area of one end of the acoustic-signal conductor.
Further objects, advantages and embodiments of the invention can be found in the subsequent description.